In an internal combustion engine, chemical reactions occur between oxygen present in air and hydrocarbon fuel. Engine works on stoichiometric air/fuel ratio when there is the correct ratio of air such that there is no excess oxygen left after combustion but in reality, the combustion process is not perfect which leads to emission of several types of pollutants. Therefore, it is important to study and gain knowledge about how much pollution is caused by these engines so that we can develop new methods for building a better environmentally friendly engine. Although, there are many other factors which cause pollution like factories, burning crackers, burning of waste material, emission of pollutants from automobiles etc yet our main focus is on pollution from cars because of the following reason - • The number of cars on roads is increasing day by day. Earlier travelling by car was considered a luxury but now it’s a necessity as they are convenient to use, reduce travelling time and are comfortable. This is one of the reasons why the number of privately-owned cars has significantly increased. The price of a car is not very high these days and can easily be afforded by a man belonging to a middle-class family. • Due to drastic increase in the number of cars not only our fuel like petrol and diesel is being used in excess which has led to depletion of these resources but also utilisation of these fuels has led to emission of pollutants like carbon monoxide, carbon dioxide, smoke excess. • Level of these pollutants specially carbon dioxide CO2 and CO has increased so much that it is unsafe in many metropolitan cities to even breathe. CO2 in such dangerous amount can cause problems like asthma and other lung related problems. © BEIESP.